1. Field of the Invention
The present invention relates to methods for producing fine spherical thermoplastic resin particles (powders). Such fine spherical thermoplastic resin particles are useful typically as cosmetic materials, fillers for coating materials, lubricants, light-diffusion additives, carriers, spacers for liquid crystal panels, and insulating fillers.
2. Description of the Related Art
Spherical thermoplastic fine resin particles are conventionally produced, for example, by a suspension polymerization method, an emulsion polymerization method, a method of mechanically dispersing or emulsifying a resin solution, or a method of precipitating fine particles from a resin solution [Japanese Unexamined Patent Application Publication (JP-A) No. 05-32795, JP-A No. 2003-171682, and JP-A No. 2004-143405]. These methods, however, require special facilities, need the use of organic solvents, have narrow applicability, and/or yield fine resin particles having only low sphericity or wide distribution of particle diameters.
JP-A No. 2004-51942 discloses a method for producing fine resin particles by melting and kneading a resin composition containing a resin component, such as a polyamide resin, and an oligosaccharide, pressing the kneaded article using a pressing machine to yield a sheet-like dispersion, cooling the dispersion, immersing the cooled dispersion in hot water to yield a suspension of resin particles, and subjecting the suspension to treatment with a membrane. This method, however, cannot significantly produce fine, highly spherical resin particles, because stress acts upon the particles during pressing of the dispersion to thereby deform the dispersed particles, and the deformed particles are cooled and solidified without mitigation of deformation.